Phase-Controlled Strategy for High-Quality Single-Source Vapor-Deposited Cs₂AgBiBr₆ Thin Films

Abstract

Environmentally friendly lead-free Cs2AgBiBr6 double perovskites have emerged as potential materials for photovoltaic applications owing to their nontoxicity and high stability. However, the low solubility of precursors in the solution method and the deviated composition in the reported sequential evaporation process are still the challenges to obtain highly pure Cs2AgBiBr6 phase films. In this work, we proposed a single-source vapor deposition process for high-quality Cs2AgBiBr6 films with an effective thermally induced phase-controlled strategy. The microstructure, composition, and photoelectric properties of Cs2AgBiBr6 films with different heat treatments were investigated, and the phase evolution of Cs2AgBiBr6 film formation was figured out. High-phase purity, uniformity, smoothness of the surface, well-defined grain structure, and desired composition stoichiometry of Cs2AgBiBr6 films led to an optimized power conversion of 1.38% for a planar device structure with excellent stability. Our results demonstrate the feasibility of employing a single-source vapor deposition technique to fabricate high-quality double perovskite thin films, which paves the way for further development of various optoelectronic devices based on these promising lead-free semiconductors.

Improved Hole Extraction and Band Alignment via Interface Modification in Hole Transport Material‐Free Ag/Bi Double Perovskite Solar Cells

“…Furthermore, the drawbacks of low selectivity and weak band alignment for HTM-free PVs are mitigated by the formation of the 2D/3D-mixed perovskite phase. Although our solar cells possess relatively low PCEs, which is a common problem for this material, [38,[41][42][43][44][45][46][47][48][49] there are promising reports of highly improved Cs 2 AgBiBr 6 , i.e., by hydrogenating the material, that will benefit from applying our approach to further boost such technology. [84]…”

“…[28,39,40] Also, the role of the Cs 2 AgBiBr 6 crystallization to form thin films for well-performing solar cells is still not understood: thin films of pristine Cs 2 AgBiBr 6 with comparable thicknesses and homogeneities result in reported solar cells with PCEs ranging from below 1% to above 2% despite equal solar cell architectures. [38,[41][42][43][44][45][46][47][48][49] Sirtl et al revealed in their work that low selectivity of the hole transport material (HTM) supports recombination and therefore hampers the solar cell performance, due to insufficient band alignment, i.e., the absence of an electron barrier between perovskite and HTM. [50] Thus, they exposed a critical bottleneck of Cs 2 AgBiBr 6 -based solar cells.…”

Carbohydrazide-Assisted Morphology and Structure Controlling for Lead-Free Cs2AgBiBr6 Double Perovskite Solar Cells

“…Halide perovskite (PVSK) materials are regarded as a promising solution to address energy and environmental challenges since the first demonstration in 2009 . Despite the noteworthy highest record of a power conversion efficiency (PCE) of 25.8% on lab-scale devices for the typical APbX 3 perovskite solar cells (PSCs), the environmental instability and lead toxicity have been major obstacles for their large-scale commercialization. , One viable strategy to resolve the toxicity is to replace the Pb content by nontoxic elements such as Sn and Ge, , while their susceptibility to oxidation leads to a more severe instability problem. , Alternatively, double perovskites with the form of A 2 B + B 3+ X 6 have been proposed for their better balance on these issues, among which Cs 2 AgBiBr 6 emerges as one highly regarded candidate with high open circuit voltage, low toxicity, and adjustable optoelectronic properties. − What is more, the inherent high decomposition enthalpy of Cs 2 AgBiBr 6 enables its superior stability compared to other lead-free perovskites …”

Straight Manipulation Annealing in a Solvent Atmosphere for Quality-Improved Cs2AgBiBr6 Perovskites

“…It prompts the multi-layer film to form a one-layer film with a large grain size and also flattens the perovskite surface, obtaining an excellent result with a large grain size, high X-ray sensitivity, and low detection limit of the device. The whole process only lasts 5 min, which is 50% shorter than the other annealing times (10 min or longer) for Cs 2 AgBiBr 6 perovskites. Besides, by investigating the remaining chemical bond, the crystal lattice of the film, and the residual atom species, we attribute the excellent performance to the recrystallization of the small-sized grain (∼100 nm) and the removal of the impurity substance, which results from the slowing down of the residual solvent evaporation and suppressing of the halide volatilization .…”